Polymer toner and method of production thereof

ABSTRACT

A polymerized toner of core-shell structure, comprising core particles composed of colored polymer particles which contain a compound having at least one &gt;C═N + &lt; structure in its molecule and a colorant, and a layer of a polymer having a glass transition temperature higher than that of a polymer component making up the core particles, said polymer layer covering each of the core particles, a production process thereof, an image forming process comprising using the polymerized toner, and an image forming apparatus containing the polymerized toner.

TECHNICAL FIELD

The present invention relates to a polymerized toner, and moreparticularly to a polymerized toner suitable for use in developing anelectrostatic image formed by an electrophotographic process,electrostatic recording process or the like, a production processthereof, an image forming process comprising using such a polymerizedtoner, and an image forming apparatus containing the polymerized toner.

BACKGROUND ART

In the electrophotographic process or electrostatic recording process,there are two-component developers composed of a toner and carrierparticles, and one-component developers composed substantially of atoner alone and making no use of any carrier particles as developers formaking electrostatic images (electrostatic latent images) visible. Theone-component developers include magnetic one-component developerscontaining magnetic powder, and non-magnetic one-component developerscontaining no magnetic powder. In the non-magnetic one-componentdevelopers, a flowability improver such as colloidal silica is oftenadded independently in order to enhance the flowability of the toner. Asthe toner, there are generally used colored particles obtained bydispersing a colorant such as carbon black and other additives in abinder resin and granulating the dispersion.

Processes for producing a toner are roughly divided into a grindingprocess and a polymerization process. In the grinding process, asynthetic resin, a colorant and optional other additives are melted andmixed, the mixture is ground, and the ground product is then classifiedso as to obtain particles having a desired particle diameter, therebyobtaining a toner. In the polymerization process, a polymerizablemonomer composition is prepared by uniformly dissolving or dispersing acolorant, a polymerization initiator and optional various additives suchas a crosslinking agent and a charge control agent in a polymerizablemonomer, the polymerizable monomer composition is dispersed in anaqueous dispersion medium containing a dispersion stabilizer by means ofa stirrer to form minute droplets of the polymerizable monomercomposition, and the dispersion containing the minute droplets is thenheated to subject the droplets to suspension polymerization, therebyobtaining colored polymer particles (polymerized toner) having a desiredparticle diameter.

In either developer, an electrostatic latent image is actually developedwith the toner. In an image forming apparatus such as anelectrophotographic apparatus or electrostatic recording apparatus, anelectrostatic latent image is generally formed on a photosensitivemember evenly charged by exposure to a light pattern, and a toner isapplied to the electrostatic latent image to form a toner image (visibleimage). The toner image is transferred to a transfer medium such astransfer paper, and the unfixed toner image is then fixed to thetransfer medium by a method such as heating, pressing or use of solventvapor. In the fixing step, the toner is often fusion-bonded to thetransfer medium by passing the transfer medium, to which the toner imagehas been transferred, through between a heating roll (fixing roll) and apress roll to press-bond the toner to the transfer medium under heat.

Images formed by an image forming apparatus such as anelectrophotographic copying machine are required to improve theirdefinition year by year. As a toner used in the image forming apparatus,a toner obtained by the grinding process has heretofore been mainlyused. The grinding process tends to form colored particles having a wideparticle diameter distribution. In order for the toner to exhibitsatisfactory developing characteristics, therefore, the ground productmust be classified to adjust the particles so as to have a particlediameter distribution limited to a certain extent. However, theclassification itself is complicated, and its yield is poor, and so thepercent yield of the toner is reduced to a great extent. Therefore, thepolymerized toner easy to control its particle diameter withoutconducting complicated production steps such as classification has cometo attract attention in recent years. According to the suspensionpolymerization process, a polymerized toner having desired particlediameter and particle diameter distribution can be obtained without needof grinding and classification. However, the conventional polymerizedtoners have involved a problem that they cannot fully meet requirementsin recent years, such as the speeding-up of copying, the formation offull-color images and energy saving.

In recent years, copying machines, printers and the like of theelectrophotographic system have been required not only to reduce demandpower, but also to achieve the speeding-up of copying or printing. Astep in which energy is particularly demanded in the electrophotographicsystem is a fixing step conducted after transferring a toner from aphotosensitive member to a transfer medium such as transfer paper. Inthe fixing step, the toner is fixed to the transfer medium by heatingand melting it. Therefore, a heating roll heated to a temperature of atleast 150° C. is used, and electric power is used as an energy sourcetherefor. There is a demand for lowering the temperature of the heatingroll from the viewpoint of energy saving. In order to lower thetemperature of the heating roll, it is necessary to use a toner capableof fixing at a temperature lower than that heretofore used. Namely, itis necessary to lower the fixing temperature of the toner itself. Theuse of the toner capable of fixing at a temperature lower than thatheretofore used permits lowering the temperature of the heating roll,and on the other hand shortening the fixing time when the temperature ofthe heating roll is not very lowered. Therefore, such a toner can meetthe speeding-up of copying and printing.

In order to meet the requirements, such as energy saving and thespeeding-up of copying, from the image forming apparatus in the designof a toner, it is only necessary to lower the glass transitiontemperature of a binder resin making up the toner. When a toner is madeup of a binder resin having a low glass transition temperature, however,the toner becomes poor in the so-called shelf stability becauseparticles themselves of the toner tend to undergo blocking duringstorage or shipment, or in a toner box of an image forming apparatus, toaggregate.

In recent years, there has been a demand for formation of bright imagesin color copying or color printing by the electrophotographic system.For example, in the full-color copying, the mere melting and softeningof toners in a fixing step to fusion-bond the toners to a transfermedium are not enough, but it is necessary to uniformly melt and mix thetoners of different colors to mix their colors. In particular, sincecolor images have come to be often used in OHP (overhead projector)sheets for presentations in various meetings or conferences, tonerimages fixed to such OHP sheets have been required to have excellentpermeability through OHP. In order to meet the excellent permeabilitythrough OHP, it is necessary for the toners to uniformly melt on atransparent OHP sheet made of a synthetic resin. Therefore, the meltviscosity of each toner at about the fixing temperature thereof must bedesigned low compared with the conventional toners. Means for loweringthe melt viscosity of the toner include a method in which the molecularweight or glass transition temperature of a binder resin used is loweredcompared with the binder resins for the conventional toners. In eithermethod, however, the toner becomes poor in shelf stability because thetoner tends to undergo blocking.

As a method for obtaining a polymerized toner having excellent fixingability, it has heretofore been proposed in, for example, JapanesePatent Application Laid-Open No. 136065/1991 to subject a polymerizablemonomer containing a colorant and a charge control agent to suspensionpolymerization in the presence of a macromonomer. The macromonomer is arelatively long-chain linear molecule having a polymerizable functionalgroup, for example, a group containing an unsaturated bond such as acarbon-carbon double bond, at its molecular chain terminal. According tothis method, the macromonomer is incorporated as a monomer unit into themolecular chain of a polymer formed. Therefore, many branchesattributable to the long-chain linear molecule of the macromonomer aregenerated in the molecular chain of the polymer. The polymer formedapparently becomes a high molecular weight polymer due to entanglementof the branches, i.e., the so-called physical crosslinking, so that theoffset resistance of the toner is improved. On the other hand, thephysical crosslinking by the macromonomer component is different fromchemical crosslinking using a crosslinking monomer such asdivinylbenzene and is of a loose crosslinked structure, and so thecrosslinked structure is easy to be broken by heating. Accordingly, thispolymerized toner is easily melted upon fixing using a heating roll andhence has excellent fixing ability. However, the polymerized toner tendsto undergo aggregation among toner particles during storage, and ishence unsatisfactory from the viewpoint of shelf stability.

According to the conventional methods for lowering the fixingtemperature of a toner and improving the uniformly melting abilitythereof, as described above, an adverse correlation that the fixingability of the resulting toner is improved, but its shelf stability islowered arises. As a means for solving this adverse correlation, therehas been proposed the so-called capsule type toner in which a toner madeup of a binder resin having a low glass transition temperature iscovered with a polymer having a high glass transition temperature,thereby improving the blocking resistance of the toner to solve theproblem of shelf stability.

As a production process of the capsule type toner, for example, JapanesePatent Application Laid-Open No. 173552/1985 has proposed a process inwhich a coating layer composed of a colorant, magnetic particles or aconductive agent and a binder resin is formed on each surface ofspherical core particles having a minute particle size by means of a jetmill. As the core particles, there are used particles formed of athermoplastic transparent resin such as an acrylate resin or styreneresin. In this publication, it has been reported that according to thisprocess, a toner of multi-layer structure, which has excellentflowability and improved functional characteristics, can be obtained.When core particles having a low glass transition temperature are usedin this method, however, the core particles themselves tend to undergoaggregation. In addition, according to this process, the coatingthickness of the binder resin is liable to thicken. Accordingly, thisprocess is difficult to provide a toner improved in both fixing abilityand uniformly melting ability while retaining its good shelf stability.

Japanese Patent Application Laid-Open No. 259657/1990 has proposed aprocess for producing a toner for electrophotography, in whichcrosslinked toner particles prepared by suspension polymerization areadded to a solution with an encapsulating polymer, a charge controlagent and a parting agent dissolved in an organic solvent, and a poorsolvent is then added to the resultant mixture to form a coating film ofthe encapsulating polymer containing the charge control agent andparting agent on each surface of the crosslinked toner particles.According to this process, however, it is difficult to obtain sphericalparticles because the solubility of the encapsulating polymer is reducedby the addition of the poor solvent to deposit the polymer on eachsurface of the crosslinked toner particles. The capsule wall formed onthe surface of each crosslinked toner particle according to this processis uneven in thickness, and moreover is relatively thick. As a result,the effects of improving development properties and fixing ability areinsufficient.

Japanese Patent Application Laid-Open No. 45558/1982 has proposed aprocess for producing a toner for developing electrostatic latentimages, in which core particles formed by polymerization are mixed withand dispersed in a 1 to 40 wt. % aqueous latex solution, and awater-soluble inorganic salt is then added to the dispersion to form acoating layer formed of fine particles obtained by emulsionpolymerization on each surface of the core particles. However, thisprocess has involved a drawback that the temperature and humiditydependence of charge properties of the resultant toner becomes high dueto the influence of a surfactant and the inorganic salt remaining on thefine particles, and the charge properties are deteriorated underhigh-temperature and high-humidity conditions in particular.

Japanese Patent Application Laid-Open No. 118758/1986 discloses aprocess for producing a toner, in which a composition containing a vinylmonomer, a polymerization initiator and a colorant is subjected tosuspension polymerization to obtain core particles, and another vinylmonomer capable of providing a polymer having hydrophilicity at leastequal to that of the resin contained in the core particles and a glasstransition temperature higher than that of said resin is polymerized inthe presence of the core particles to form shell on each of the coreparticles. According to this process, however, the vinyl monomer forforming the shell is caused to be adsorbed on each of the core particlesto grow it, so that in many cases, it may be difficult to create a clearcore-shell structure because the vinyl monomer absorbed in the interiorof the core particles is polymerized. Accordingly, this process isdifficult to provide a toner sufficiently improved in shelf stability.In addition, in order to create a clear core-shell structure so as toimprove the shelf stability, it has been necessary to thicken thethickness of the shell.

Japanese Patent Application Laid-Open No. 128908/1995 discloses aprocess for directly producing a polymerized toner by subjecting amonomer composition containing a polymerizable monomer, a colorant and aparting agent to suspension polymerization in an aqueous dispersionmedium, the process comprising the steps of causing the parting agent tocontain in a proportion of 10 to 40 parts by weight per 100 parts byweight of the polymerizable monomer and removing the parting agent onthe surface of the toner formed after completion of the polymerizationstep. According to this process, the parting agent on the surface of thetoner is removed, so that staining due to attachment of the partingagent (wax) to a developing drum, a photosensitive drum, a transfer drumand/or the like can be reduced. However, this process cannot fullyimprove the shelf stability, fixing temperature and the like of thetoner, and the resulting toner tends to cause fogging, lowering of imagedensity, etc.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a polymerized tonerwhich has a low fixing temperature and uniformly melting ability, and isexcellent in shelf stability (blocking resistance), low in thedependence of charge level on environment, and hard to cause fogging,lowering of image density, etc., and a production process thereof.

Another object of the present invention is to provide a polymerizedtoner which can meet the speeding-up of copying or printing, theformation of full-color images, and energy saving, and a productionprocess thereof.

A further object of the present invention is to provide a polymerizedtoner capable of forming a toner image which exhibits excellentpermeability (permeability through OHP) when conducting printing on anOHP sheet with the toner and fixing the resulting image thereto, and aproduction process thereof.

A still further object of the present invention is to provide an imageforming process comprising using the polymerized toner having suchexcellent various properties, and an image forming apparatus in whichsaid polymerized toner is contained.

The present inventors have carried out an extensive investigation with aview toward overcoming the above-described problems involved in theprior art. As a result, it has been found that when a compound having atleast one >C═N⁺< structure in its molecule is caused to be contained incore particles composed of colored polymer particles, and apolymerizable monomer for shell, which is capable of forming a polymerhaving a glass transition temperature higher than that of the polymercomponent making up the core particles, is polymerized in the presenceof the core particles to form a polymer layer serving as shell on eachsurface of the core particles, thereby producing a capsule typepolymerized toner (polymerized toner of core-shell structure), thepolymerized toner can be provided as a toner which has a low fixingtemperature and uniformly melting ability, and is excellent in shelfstability (blocking resistance). This polymerized toner is low in thedependence of charge level on environment, and hard to cause fogging,deterioration of image density, etc., and exhibits excellentpermeability through OHP. The present invention has been led tocompletion on the basis of these findings.

According to the present invention, there is thus provided a polymerizedtoner of core-shell structure, comprising core particles composed ofcolored polymer particles which contain a compound having at least one>C═N⁺< structure in its molecule and a colorant, and a layer of apolymer having a glass transition temperature higher than that of apolymer component making up the core particles, said polymer layercovering each of the core particles.

According to the present invention, there is also provided a process forproducing a polymerized toner of core-shell structure, which comprisesthe steps of (I) polymerizing a polymerizable monomer compositioncontaining a compound having at least one >C═N⁺< structure in itsmolecule, a colorant and a polymerizable monomer for core to preparecore particles formed of colored polymer particles; and then (II)polymerizing a polymerizable monomer for shell, which is capable offorming a polymer having a glass transition temperature higher than thatof a polymer component making up the core particles, in the presence ofthe core particles in an aqueous dispersion medium to form shell whichis formed of a polymer layer and covers each of the core particles.

According to the present invention, there is further provided an imageforming process, comprising the steps of applying a toner to the surfaceof a photosensitive member, on which an electrostatic latent image hasbeen formed, to make the latent image visible, and then transferring thevisible image to a transfer medium, wherein the above-describedpolymerized toner of core-shell structure is used as the toner.

According to the present invention, there is still further provided animage forming apparatus, comprising a photosensitive member, a means forcharging the surface of the photosensitive member, a means for formingan electrostatic latent image on the surface of the photosensitivemember, a means for receiving a toner, a means for supplying the tonerto develop the electrostatic latent image on the surface of thephotosensitive member, thereby forming a toner image, and a means fortransferring the toner image from the surface of the photosensitivemember to a transfer medium, wherein the means for receiving the tonercontains the above-described polymerized toner of core-shell structure.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view illustrating an example of an imageforming apparatus to which a polymerized toner according to the presentinvention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

(Compound having at least one >C═N⁺< structure in its molecule).

In the present invention, a compound having, in its molecule, at leastone structure represented by the formula (1):

>C═N^(⊕)<  (1)

is caused to be contained in core particles.

A typical example of this compound includes a heterocycle-containingcompound having the bond represented by the formula (1) on the end ofits molecular chain or within its molecular chain (in its principalchain or side chain).

As examples of such a heterocycle-containing compound, may be mentionedcompound represented by the following formulae (2) to (11). In theseformulae, R¹ means a principal chain of each compound, R² denotes aprincipal chain of the compound, a hydrogen atom or a hydrocarbon grouphaving at most 6 carbon atoms, and R³, R⁴ and R⁵ are independently ahydrocarbon group. In the hydrocarbon group, at least part of hydrogenatoms in its molecule may be substituted by a substituent such as ahalogen atom, or a nitro, epoxy, carboxyl or hydroxyether group. X⁻means an anion.

Formula (2):

Formula (3):

The compounds represented by the formulae (2) and (3) are compoundshaving a 1,3-oxazine structure typified by a 1,3-oxazine ring,4H,5H-1,3-oxazine ring or the like, in which the nitrogen atom in theheterocyclic ring has been converted into a quaternary ammonium salt.

Formula (4):

Formula (5):

The compounds represented by the formulae (4) and (5) are compoundshaving a 1,3-thiazine ring or 5H,6H-1,3-thiazine ring, in which thenitrogen atom in the thiazine ring has been converted into a quaternaryammonium salt.

Formula (6):

Formula (7):

The compounds represented by the formulae (6) and (7) are compoundshaving an isoxazole ring or 4H,5H-isoxazole ring, in which the nitrogenatom in the isoxazole ring has been converted into a quaternary ammoniumsalt.

Formula (8):

Formula (9):

The compounds represented by the formulae (8) and (9) are compoundshaving a 1,2-diazole ring or 4H,5H-1,2-diazole ring, in which thenitrogen atom in the diazole ring has been converted into a quaternaryammonium salt.

Formula (10):

Formula (11):

The compounds represented by the formulae (10) and (11) are compoundshaving a 2H-pyrrole ring or 2H,3H,4H-pyrrole ring, in which the nitrogenatom in the pyrrole ring has been converted into a quaternary ammoniumsalt.

Other typical examples of the compound having at least one structurerepresented by the formula (1) in its molecule include, as polymers,modified polymers obtained by reacting an organic compound, which willbe described subsequently, with {circle around (1+L )} a living anionicpolymer obtained by polymerizing a monomer polymerizable by a catalystbased on a metal such as an alkali metal or alkaline earth metal(so-called anionic polymerization catalyst), and having an ion of such ametal at its terminal, or {circle around (2+L )} an unsaturated polymerhaving double bonds in its polymer chain or side chain in the presenceof an alkali metal, alkaline earth metal, transition metal or halidethereof (Lewis acid), and then hydrolyzing the reaction product; andhydrogenated modified polymers obtained by hydrogenating double bonds inthe modified polymers thus obtained (Japanese Patent ApplicationLaid-Open Nos. 162604/1983, 137913/1985 and 89932/1991).

As examples of the organic compound reacted with {circle around (1+L )}the living polymer or {circle around (2+L )} the metal-added unsaturatedpolymer, may be mentioned N-substituted lactams such asN-methyl-β-propiolactam, N-t-butyl-β-propiolactam,N-phenyl-β-propiolactam, N-methoxyphenyl-β-propiolactam,N-naphthyl-β-propiolactam, N-methyl-2-pyrrolidone,N-t-butyl-2-pyrrolidone, N-phenyl-2-pyrrolidone,N-methoxyphenyl-2-pyrrolidone, N-vinyl-2-pyrrolidone,N-benzyl-2-pyrrolidone, N-naphthyl-2-pyrrolidone,N-methyl-5-methyl-2-pyrrolidone, N-t-butyl-5-methyl-2-pyrrolidone,N-phenyl-5-methyl-2-pyrrolidone, N-methyl-3,3′-dimethyl-2-pyrrolidone,N-phenyl-3,3′-dimethyl-2-pyrrolidone,N-t-butyl-3,3′-dimethyl-2-pyrrolidone, N-methyl-2-piperidone,N-t-butyl-2-piperidone, N-phenyl-2-piperidone,N-methoxyphenyl-2-piperidone, N-vinyl-2-piperidone,N-benzyl-2-piperidone, N-naphthyl-2-piperidone,N-methyl-5-methyl-2-piperidone, N-t-butyl-5-methyl-2-piperidone,N-phenyl-5-methyl-2-piperidone, N-methyl-3,3′-dimethyl-2-piperidone,N-phenyl-3,3′-dimethyl-2-piperidone,N-t-butyl-3,3′-dimethyl-2-piperidone, N-methyl-ε-caprolactam,N-phenyl-ε-caprolactam, N-methoxylphenyl-ε-caprolactam,N-vinyl-ε-caprolactam, N-benzyl-ε-caprolactam, N-naphthyl-ε-caprolactam,N-methyl-ω-laurylolactam, N-phenyl-ω-laurylolactam,N-t-butyl-ω-laurylolactam, N-vinyl-ω-laurylolactam andN-benzyl-ω-laurylolactam, and their corresponding thiolactams; andN-substituted ethylene ureas such as 1,3-divinylethylene urea,1,3-diphenylethylene urea, 1,3-di-t-butylethylene urea and1,3-dimethylethylene urea, and their corresponding N-substitutedthioethylene ureas. These organic compounds are compounds having a bondrepresented by the formula (12):

wherein Y is an oxygen atom or sulfur atom, in their molecules.

Besides the direct reaction of the compound having the bond representedby the formula (12) and capable of imparting the bond represented by theformula (1) when bonded to the resin, an amine and an acid halide mayalso be allowed to react using an alkali metal, alkaline earth metal ortransition metal, or a salt thereof as a catalyst. When the acid halideis a carboxylic acid halide, a compound represented by the formula (2)or (3) is provided. When it is a thiocarboxylic acid on the other hand,a compound represented by the formula (4) or (5) is provided.

Specific examples of the amine include benzylidenealkylamine such asbenzylideneethylamine, benzylidenepropylamine, benzylidenebutylamine,benzylidenehexylamine, benzylideneoctylamine andbenzylidenestearylamine; and alkylidenealkylamines such asethylidenepropylamine, ethylideneisobutylamine, propylideneethylamineand propylidenenonylamine. Specific examples of the acid halide includesaturated fatty acid halides such as acetyl chloride, valeryl bromide,capryl chloride and lauryl chloride; unsaturated fatty acid such aschloride crotonate and bromide oleate; aromatic carboxylic acid halidessuch as benzoyl chloride and benzoyl bromide; and saturatedthiocarboxylic acid halides such as thioacetyl bromide and thiopropionylchloride.

Examples of other organic compounds than the above-mentioned compoundsinclude N-substituted aminoketones such as 4-dimethylaminobenzophenone,4-diethylaminobenzophenone, 4-di-t-butylaminobenzophenone,4-diphenyl-aminobenzophenone, 4,4′-bis-(dimethylamino)benzophenone,4,4′-bis(diethylamino)benzophenone,4,4′-bis(d-t-butylamino)-benzophenone,4,4′-bis(diphenylamino)benzophenone, 4,4′-bis(divinylamino)benzophenone,4-dimethylaminoacetophenone, 4-diethylaminoacetophenone,1,3-bis(diphenylamino)-2-propanone and1,7-bis(methylethylamino)-4-heptanone, and their correspondingN-substituted aminothioketones; and N-substituted aminoaldehydes such as4-dimethylaminobenzaldehyde, 4-diphenylaminobenzaldehyde and4-divinylaminobenzaldehyde, and their corresponding N-substitutedaminothioaldehydes.

The proportion of the compound having at least one structure representedby the formula (1) in its molecule to be incorporated is generallywithin a range of 0.05 to 300 parts by weight, preferably 0.5 to 200parts by weight per 100 parts by weight of the colorant. If theproportion of this compound is too low, the dispersibility of thecolorant becomes insufficient, and so it is difficult to achieve theexpected effect. If the proportion of the compound is too high on theother hand, the dispersing effect of the compound on the colorant issaturated, which is uneconomical. Such a compound is dispersed togetherwith the colorant in the polymer making up the core particles. Thecompound and colorant are preferably dispersed in the polymer making upthe core particles by mixing and dispersing them in the polymerizablemonomer for core and subjecting the resultant dispersion to suspensionpolymerization.

(Colorant)

As examples of the colorant, may be mentioned dyes and pigment such ascarbon black, titanium white, Nigrosine Base, aniline blue, ChalcoilBlue, chrome yellow, ultramarine blue, Orient Oil Red, PhthalocyanineBlue and Malachite Green oxalate; and magnetic powders such as cobalt,nickel, diiron trioxide, triiron tetroxide, manganese iron oxide, zinciron oxide and nickel iron oxide. Besides the above-mentioned colorants,the following various colorants may be mentioned.

Examples of colorants for magnetic color toners include C.I. Direct Red1, C.I. Direct Red 4, C.I. Acid Red 1, C.I. Basic Red 1, C.I. MordantRed 30, C.I. Direct Blue 1, C.I. Direct Blue 2, C.I. Acid Blue 9, C.I.Acid Blue 15, C.I. Basic Blue 3, C.I. Basic Blue 5, C.I. Mordant Blue 7,C.I. Direct Green 6, C.I. Basic Green 4 and C.I. Basic Green 6.

Examples of pigments include chrome yellow, cadmium yellow, Mineral FastYellow, Navel Yellow, Naphthol Yellow S, Hansa Yellow G, PermanentYellow NCG, Tartrazine Lake, chrome orange, molybdenum orange, PermanentOrange GTR, Pyrazolone Orange, Benzidine Orange G, cadmium red,Permanent Red 4R, Watchung Red Ca, eosine lake, Brilliant Carmine 3B,manganese violet, Fast Violet B, Methyl Violet Lake, iron blue, cobaltblue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, FastSky Blue, Indanthrene Blue BC, chrome green, chromium oxide, PigmentGreen B, Malachite Green Lake and Final Yellow Green G.

Examples of magenta color pigments for full-color toners include C.I.Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48, 49, 50, 51, 52,53, 54, 55, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114,122, 123, 163, 202, 206, 207 and 209; C.I. Pigment Violet 19; and C.I.Vat Red 1, 2, 10, 13, 15, 23, 29 and 35.

Examples of magenta dyes include oil-soluble dyes such as C.I. SolventRed 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109 and 121;C.I. Disperse Red 9; C.I. Solvent Violet 8, 13, 14, 21 and 27; and C.I.Disperse Violet 1; and besides basic dyes such as C.I. Basic Red 1, 2,9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38,39 and 40; and C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27 and28.

Examples of cyan color pigments for full-color toners include C.I.Pigment Blue 2, 3, 15, 16 and 17; C.I. Vat Blue 6; C.I. Acid Blue 45;and copper phthalocyanine pigments with 1 to 5 phthalimidomethyl groupsadded to a phthalocyanine skeleton.

Examples of yellow color pigments for full-color toners include C.I.Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 23,65, 73, 83, 138 and 180; and C.I. Vat Yellow 1, 3 and 20.

Among the colorants, the dyes or pigments are used in a proportion ofgenerally 0.1 to 20 parts by weight, preferably 0.5 to 10 parts byweight per 100 parts by weight of the polymerizable monomer for core.The magnetic powder is used in a proportion of generally 1 to 100 partsby weight, preferably 5 to 50 parts by weight per 100 parts by weight ofthe polymerizable monomer for core.

(Core particles)

The core particles useful in the practice of the present inventiongenerally comprise, as a polymer component, a polymer such as apolyester resin or a (meth)acrylic ester-styrene copolymer and arepreferably composed of colored polymer particles comprising the(meth)acrylic ester-styrene copolymer.

In the polymerized toner according to the present invention, the volumeaverage particle diameter (dv) of the core particles is generally 1 to20 μm, preferably 1 to 10 μm. If the volume average particle diameter ofthe core particles is too great, the resolution of an image formed withsuch a toner tends to lower. The ratio (dv)/(dp) of the volume averageparticle diameter (dv) to a number average particle diameter (dp) in thecore particles is generally at most 1.7, preferably at most 1.5.

No particular limitation is imposed on the production process of thecore particles used in the present invention, and any of emulsionpolymerization, suspension polymerization, precipitation polymerizationand soap-free polymerization may be used. However, a process comprisingsubjecting a polymerizable monomer for core to suspension polymerizationis preferred in that the colorant can be caused to be uniformlycontained in each of core particles formed, and the fixing ability ofthe resulting toner is improved.

The polymerizable monomer for core used in the present invention is suchthat can form a polymer having a glass transition temperature of 80° C.or lower, preferably 10 to 70° C., more preferably 20 to 60° C. As thepolymerizable monomer for core, there may be used one of such monomersor any combination of such monomers. If the polymerizable monomer forcore is a monomer capable of forming a polymer having a glass transitiontemperature exceeding 80° C., the resulting polymerized toner comes tohave a higher fixing temperature and deteriorated permeability throughOHP and can not meet the speeding-up of copying or printing.

The glass transition temperature (Tg) of the polymer is a calculatedvalue (referred to as calculated Tg) calculated out according to thekind(s) and proportion(s) of monomer(s) used. When the monomer used isone, the Tg of a homopolymer formed from this monomer is defined as Tgof the polymer in the present invention. For example, the Tg ofpolystyrene is 100° C. Therefore, when styrene is used as a monomer byitself, the monomer can be said to form a polymer having a Tg of 100° C.When monomers used are two or more, and the polymer formed is acopolymer, the Tg of the copolymer is calculated out according to thekinds and proportions of the monomers used. For example, when 78 wt. %of styrene and 22 wt. % of n-butyl acrylate are used as monomers, themonomers can be said to form a polymer having a Tg of 50° C. because theTg of a styrene-n-butyl acrylate copolymer formed at this monomer ratiois 50° C.

The definition of “a polymerizable monomer for core, which is capable offorming a polymer having a glass transition temperature of 80° C. orlower” does not mean that when plural monomers are used, the individualmonomers must form respective polymers having a Tg of 80° C. or lower.When one monomer is used, the Tg of a homopolymer formed from themonomer must be 80° C. or lower. When two or more monomers are used,however, it is only necessary for the Tg of a copolymer formed from themonomer mixture to be 80° C. or lower. Therefore, those which separatelyform a homopolymer having a Tg higher than 80° C. may be contained inthe monomer mixture. For example, although the Tg of a styrenehomopolymer is 100° C., styrene may be used as a component of thepolymerizable monomer for core so far as a copolymer having a Tg of 80°C. or lower can be formed by using a mixture of styrene with a monomer(for example, n-butyl acrylate) which forms a homopolymer having a lowTg.

In the present invention, vinyl monomers are generally used as thepolymerizable monomer for core. Various kinds of vinyl monomers are usedeither singly or in combination of two or more thereof so as to adjustthe Tg of the resulting polymer within the desired range.

Examples of the vinyl monomers used in the present invention includestyrenic monomers such as styrene, vinyltoluene and α-methylstyrene;acrylic acid and methacrylic acid; (meth)acrylic acid derivatives suchas methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,2-ethylhexyl acrylate, dimethylaminoethyl acrylate, methyl methacrylate,ethyl methacrylate, propyl methacrylate, butyl methacrylate,2-ethylhexyl methacrylate, dimethylaminoethyl methacrylate,acrylonitrile, methacrylonitrile, acrylamide and methacrylamide;ethylenically unsaturated monoolefins such as ethylene, propylene andbutylene; vinyl halides such as vinyl chloride, vinylidene chloride andvinyl fluoride; vinyl esters such as vinyl acetate and vinyl propionate;vinyl ethers such as vinyl methyl ether and vinyl ethyl ether; vinylketones such as vinyl methyl ketone and methyl isopropenyl ketone; andnitrogen-containing vinyl compounds such as 2-vinylpyridine,4-vinylpyridine and N-vinylpyrrolidone. These vinyl monomers may be usedeither singly or in any combination thereof.

Of these, a combination of a styrenic monomer with a (meth)acrylic acidderivative is preferably used as the polymerizable monomer for core. Aspreferable specific examples thereof, may be mentioned combinations ofstyrene with butyl acrylate (i.e., n-butyl acrylate), and styrene with2-ethylhexyl acrylate.

It is preferred from the viewpoint of improvement in the shelf stabilityof the resulting polymerized toner to use a crosslinking monomertogether with the vinyl monomer(s). Examples of the crosslinking monomerinclude aromatic divinyl compounds such as divinylbenzene,divinylnaphthalene and derivatives thereof; diethylenic esters ofunsaturated carboxylic acids such as ethylene glycol dimethacrylate anddiethylene glycol dimethacrylate; divinyl compounds such asN,N-divinylaniline and divinyl ether; and compounds having at leastthree vinyl groups. These crosslinking monomers may be used eithersingly or in any combination thereof. In the present invention, it isdesirable that the crosslinking monomer be used in a proportion ofgenerally 0.01 to 5 parts by weight, preferably 0.1 to 2 parts by weightper 100 parts by weight of the polymerizable monomer for core.

In the present invention, it is preferred to use a macromonomer togetherwith the polymerizable monomer for core in that the balance between thelow-temperature fixing ability and shelf stability of the resultingpolymerized toner is improved. The macromonomer (also referred to asmacromer) used in the present invention is a relatively long-chainlinear molecule having a polymerizable functional group (for example, agroup containing an unsaturated bond such as a carbon-carbon doublebond) at its molecular chain terminal. The macromonomer is preferably anoligomer or polymer having a polymerizable vinyl functional group at itsmolecular chain terminal and a number average molecular weight ofgenerally 1,000 to 30,000. If a macromonomer having a too low numberaverage molecular weight is used, the surface part of the resultingpolymerized toner becomes soft, and its shelf stability shows a tendencyto deteriorate. If a macromonomer having a too high number averagemolecular weight is used on the other hand, the melt property of themacromonomer becomes poor, resulting in a polymerized toner deterioratedin fixing ability.

Examples of the polymerizable vinyl functional group which themacromonomer has at its molecular chain terminal include an acryloylgroup and a methacryloyl group, with the methacryloyl group beingpreferred from the viewpoint of easy copolymerization.

The macromonomer used in the present invention preferably has a glasstransition temperature higher than that of a polymer obtained bypolymerizing the polymerizable monomer for core. A difference in Tgbetween the polymer obtained by polymerizing the polymerizable monomerfor core and the macromonomer may be relative. For example, when thepolymerizable monomer for core is such that forms a polymer having a Tgof 70° C., it is only necessary for the macromonomer to have a Tg higherthan 70° C. When the polymerizable monomer for core is such that forms apolymer having a Tg of 20° C., the macromonomer may also be that havinga Tg of, for example, 60° C. The Tg of the macromonomer is a valuemeasured by means of an ordinary measuring device such as a differentialscanning calorimeter (DSC).

As examples of the macromonomer used in the present invention, may bementioned polymers obtained by polymerizing styrene, styrenederivatives, methacrylic esters, acrylic esters, acrylonitrile andmethacrylonitrile either singly or in combination of two or moremonomers thereof; macromonomers having a polysiloxane skeleton; andthose disclosed in Japanese Patent Application Laid-Open No.203746/1991, pages 4 to 7. Of these macromonomers, hydrophilicmacromonomers, in particular, polymers obtained by polymerizingmethacrylic esters or acrylic esters either singly or in combination oftwo or more monomers thereof are preferred in the present invention.

The amount of the macromonomer used is generally 0.01 to 10 parts byweight, preferably 0.03 to 5 parts by weight, more preferably 0.05 to 1part by weight per 100 parts by weight of the polymerizable monomer forcore. If the amount of the macromonomer used is too little, it isdifficult to improve the shelf stability and fixing ability of theresulting polymerized tone in a well balanced relation. If the amount ofthe macromonomer used is too great, the resulting polymerized tonershows a tendency to deteriorate its fixing ability.

In the present invention, it is preferred that the core particles beprovided by subjecting the polymerizable monomer for core as apolymerizable component, and optionally the macromonomer and thecrosslinking monomer to suspension polymerization.

The suspension polymerization is generally performed in an aqueousmedium containing a dispersion stabilizer. More specifically, thesuspension polymerization is conducted by mixing a vinyl monomer,optional macromonomer and crosslinking monomer, a colorant, a compoundhaving at least one bond represented by the formula (1) in its molecule,a radical polymerization initiator, and other additives, uniformlydispersing them by means of a ball mill or the like to prepare a liquidmixture (hereinafter, may be referred to as the stock dispersion),pouring the stock dispersion into an aqueous medium containing adispersion stabilizer to disperse the stock dispersion in the aqueousmedium by means of a mixer having high shearing force, thereby formingminute droplets of the stock dispersion, and then polymerizing them at atemperature of generally 30 to 200° C.

When the radical polymerization initiator is not contained in the stockdispersion, the polymerization initiator may be poured into the aqueousmedium containing the dispersion stabilizer with stirring after pouringthe stock dispersion into the aqueous medium and before the formation ofminute droplets, thereby preparing a polymerizable monomer compositionfor core.

The time the radical polymerization initiator is added varies accordingto the intended toner particles, but is generally a point of time thedroplet diameter (volume average droplet diameter) of primary dropletsformed by the stirring of the stock dispersion has amounted to generally50 to 1,000 μm, preferably 100 to 500 μm. If the time period from thepouring and stirring of the stock dispersion containing no initiator tothe addition of the radical polymerization initiator is long, theformation of the minute droplets is completed, so that the monomer andthe like in the stock dispersion containing no initiator cannot beuniformly mixed with the oil-soluble polymerization initiator, resultingin the difficulty of making the resin properties of the resultingindividual polymerized toner particles, such as polymerization degreeand crosslinking degree, even. Therefore, the point of time the radicalpolymerization initiator is added is generally within 24 hours,preferably 12 hours, more preferably 3 hours after the pouring of thestock dispersion containing no initiator in a large-scale productionlike plant or the like, and generally within 5 hours, preferably 3hours, more preferably 1 hour in a small-scale production at alaboratory level though it somewhat varies according to the scale ofreaction and droplet diameter.

The temperature of the aqueous dispersion medium between the addition ofthe radical polymerization initiator and the subsequent formation ofminute droplets (i.e., before the initiation of polymerization) isregulated within a range of generally 10 to 40° C., preferably 20 to 30°C. If this temperature is too high, the polymerization reaction ispartially initiated within the system. If the temperature is too low onthe other hand, the flowability of the system is lowered when thedroplets are formed by stirring, so that there is a possibility thatsuch a too low temperature may interfere with the formation of thedroplets.

Incidentally, the colorant may also be subjected to a surface treatmentwith the compound having at least one bond represented by the formula(1) in its molecule in advance and then mixed with the vinyl monomer andthe like.

A dispersing agent (dispersion stabilizer) preferably used in thepresent invention is that containing colloid of a hardly water-solublemetallic compound. As examples of the hardly water-soluble metalliccompound, may be mentioned sulfates such as barium sulfate and calciumsulfate; carbonates such as barium carbonate, calcium carbonate andmagnesium carbonate; phosphates such as calcium phosphate; metal oxidessuch as aluminum oxide and titanium oxide; and metal hydroxides such asaluminum hydroxide, magnesium hydroxide and ferric hydroxide. Dispersingagents containing the colloid of a hardly water-soluble metal hydroxideamong these are preferred because the particle diameter distribution ofthe resulting polymer particles can be narrowed, and the brightness orsharpness of an image formed from such a polymerized toner is enhanced.In particular, when the crosslinking monomer is not copolymerized, thedispersing agent containing the colloid of the hardly water-solublemetal hydroxide is preferably used for improving the fixing ability andshelf stability of the resulting polymerized toner.

The dispersion stabilizer containing the colloid of the hardlywater-soluble metal hydroxide is not limited by the production processthereof. However, it is preferred to use colloid of a hardlywater-soluble metal hydroxide obtained by adjusting the pH of an aqueoussolution of a water-soluble polyvalent metallic compound to 7 or higher,in particular, colloid of a hardly water-soluble metal hydroxide formedby reacting a water-soluble polyvalent metallic compound with an alkalimetal hydroxide in an aqueous phase.

The colloid of the hardly water-soluble metal hydroxide used in thepresent invention preferably has number particle diameter distributions,D₅₀ (50% cumulative value of number particle diameter distribution) ofat most 0.5 μm and D₉₀ (90% cumulative value of number particle diameterdistribution) of at most 1 μm. If the particle diameter of the colloidis too great, the stability of the polymerization is broken, and theshelf stability of the resulting polymerized toner is deteriorated.

The dispersing agent is generally used in a proportion of 0.1 to 20parts by weight per 100 parts by weight of the polymerizable monomer forcore. If the proportion of the dispersing agent used is too low, it isdifficult to achieve sufficient polymerization stability, so that theresulting polymer tends to aggregate. If the proportion of thedispersing agent used is too high on the other hand, the viscosity ofthe aqueous dispersion medium becomes too high, and the particlediameter distribution of the resulting polymerized toner becomes wide.It is hence not preferred to use the dispersing agent in such a too lowor high proportion.

In the present invention, a dispersing agent containing a water-solublepolymer may be used as needed. As examples of the water-soluble polymer,may be mentioned polyvinyl alcohol, methyl cellulose and gelatin. In thepresent invention, there is no need to use any surfactant. However, asurfactant may be used for the purpose of stably conducting thepolymerization so far as the dependence of the charge properties of theresulting polymerized toner on environment does not become high.

As examples of the radical polymerization initiator, may be mentionedpersulfates such as potassium persulfate and ammonium persulfate; azocompounds such as 4,4′-azobis(4-cyanovaleric acid),2,2′-azobis-(2-methylpropionate) dimethyl, 2,2′-azobis(2-amidinopropane)bihydrochloride,2,2′-azobis-2-methyl-N-1,1-bis(hydroxymethyl)-2-hydroxy-ethylpropionamide,2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile and1,1′-azobis(1-cyclohexanecarbonitrile); and peroxides such as methylethyl peroxide, di-t-butyl peroxide, acetyl peroxide, dicumyl peroxide,lauroyl peroxide, benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate,di-isopropyl peroxydicarbonate and di-t-butyl peroxyisophthalate. Redoxinitiators composed of combinations of these polymerization initiatorswith a reducing agent may also be mentioned.

Of these radical polymerization initiators, oil-soluble radicalinitiators are preferred, with oil-soluble radical initiators selectedfrom among organic peroxides whose ten-hour half-life temperatures are60 to 80° C., preferably 65 to 80° C. and whose molecular weights are250 or lower being particularly preferred. Of the oil-soluble radicalinitiators, t-butyl peroxy-2-ethylhexanoate is particularly preferredbecause the resulting polymerized toner scarcely gives odor uponprinting and barely causes environmental destruction by volatilecomponents such as odor.

The amount of the polymerization initiator used is generally 0.001 to 3wt. % based on the aqueous medium. If the amount of the polymerizationinitiator used is less than 0.001 wt. %, the rate of polymerizationbecomes slow. Any amount exceeding 3 wt. % is not economical.

In the present invention, as needed, various kinds of additives such asa molecular weight modifier and a parting agent may be used by mixingthem with the polymerizable monomer for core.

Examples of the molecular weight modifier include mercaptans such ast-dodecylmercaptan, n-dodecylmercaptan and n-octylmercaptan; andhalogenated hydrocarbons such as carbon tetrachloride and carbontetrabromide. These molecular weight modifiers may be added before theinitiation of the polymerization or in the course of the polymerization.The molecular weight modifier is used in a proportion of generally 0.01to 10 parts by weight, preferably 0.1 to 5 parts by weight per 100 partsby weight of the polymerizable monomer for core.

As examples of the parting agent, may be mentioned low molecular weightpolyolefins such as low molecular weight polyethylene, low molecularweight polypropylene and low molecular weight polybutylene; paraffinwaxes; and polyfunctional ester compounds. As the parting agents used inthe present invention, the polyfunctional ester compounds are preferred,with polyfunctional ester compounds formed of a trifunctional or stillhigher polyfunctional polyhydric alcohol and a carboxylic acid beingparticularly preferred.

Examples of the trifunctional or still higher polyfunctional polyhydricalcohol include aliphatic alcohols such as glycerol, pentaerythritol andpentaglycerol; alicyclic alcohols such as phloroglucitol, quercitol andinositol; aromatic alcohols such as tris-(hydroxymethyl)benzene;saccharides such as D-erythrose, L-arabinose, D-mannose, D-galactose,D-fructose, L-rhamnose, saccharose, maltose and lactose; and sugaralcohols such as erythoritol, D-threitol, L-arabitol, adonitol andxylitol. Of these, pentaerythritol is preferred.

Examples of the carboxylic acid include aliphatic carboxylic acids suchas acetic acid, butyric acid, caproic acid, enanthic acid, caprylicacid, pelargonic acid, capric acid, undecanoic acid, lauric acid,myristic acid, stearic acid, margaric acid, arachidic acid, ceroticacid, melissic acid, erucic acid, brassidic acid, sorbic acid, linolicacid, linolenic acid, behenolic acid, tetrolic acid and ximenynic acid;alicyclic carboxylic acids such as cyclohexanecarboxylic acid,hexahydroisophthalic acid, hexahydroterephthalic acid and3,4,5,6-tetrahydrophthalic acid; and aromatic carboxylic acids such asbenzoic acid, toluic acid, cuminic acid, phthalic acid, isophthalicacid, terephthalic acid, trimesic acid, trimellitic acid andhemimellitic acid. Of these, carboxylic acids having, preferably, 10 to30 carbon atoms, more preferably, 13 to 25 carbon atoms are preferred,and aliphatic carboxylic acids having the said number of carbon atomsare more preferred. Among the aliphatic carboxylic acids, stearic acidand myristic acid are particularly preferred.

In the polyfunctional ester compound used as a parting agent in thepresent invention, the carboxylic acids bonded to the trifunctional orstill higher polyfunctional polyhydric alcohol may be the same ordifferent from one another. It is preferred that a difference betweenthe maximum value and the minimum value in the number of carbon atomsamong plural carboxylic acids bonded be at most 9, preferably at most 5.

As specific examples of the polyfunctional ester compound, may bementioned pentaerythritol tetrastearate, pentaerythritol tetramyristateand glycerol triarachidate. It is preferred that the polyfunctionalester compound be easily soluble in the polymerizable monomer for core.Among the polyfunctional ester compounds, pentaerythritol tetrastearateand pentaerythritol tetramyristate are preferred, with pentaerythritoltetramyristate being particularly preferred. In the case where a partingagent is mixed with the polymerizable monomer, the conventional waxesmust be dispersed in the monomer by grinding or melting them. However,pentaerythritol tetramyristate or the like among the polyfunctionalester compounds is easily soluble in the polymerizable monomer even atordinary temperature, so that the polymerizable monomer composition canbe prepared with ease, and moreover a polymerized toner excellent invarious properties can be provided.

The parting agent is used in a proportion of generally 0.1 to 40 partsby weight, preferably 1 to 20 parts by weight per 100 parts by weight ofthe polymerizable monomer. If the amount of the parting agent used istoo little, the effect of improving the low-temperature fixing abilitybecomes little. If the amount is too great, the blocking resistance ofthe resulting polymerized toner is deteriorated.

A lubricant such as oleic acid or stearic acid; a dispersion aid such asa silane or titanium coupling agent; and/or the like may also be usedwith a view toward uniformly dispersing the colorant in the coreparticles. Such a lubricant or dispersion aid is generally used in aproportion of about 1/1,000 to 1/1 based on the weight of the colorant.

In the polymerization for obtaining the core particles used in thepresent invention, the conversion of the polymerizable monomer into apolymer is generally controlled to at least 80%, preferably at least85%, more preferably at least 90%. If the conversion into the polymer islower than 80%, a great amount of the polymerizable monomer for coreremains unreacted, so that each surface of the resultant core particlesis covered with a copolymer of a polymerizable monomer for shell and thepolymerizable monomer for core even when the polymerizable monomer forshell is added to conduct polymerization. Therefore, a difference in Tgbetween the core particles and the shell becomes small, and so theresulting polymerized toner tends to lower its shelf stability.

(Formation of shell)

In the present invention, a polymerizable monomer for shell ispolymerized in the presence of the core particles to form a polymerlayer (shell) on each surface of the core particles.

The polymerizable monomer for shell used in the present invention issuch that can form a polymer having a glass transition temperaturehigher than that of the polymer component making up the core particles.A difference in Tg between the polymer obtained by the polymerizablemonomer for shell and the polymer component (usually, the polymerobtained by the polymerizable monomer for core) making up the coreparticles is relative.

As the polymerizable monomer for shell, there may be generally usedmonomers capable of forming a polymer having a glass transitiontemperature higher than 80° C., such as styrene and methyl methacrylate,either singly or in combination of two or more monomers thereof. Whenthe glass transition temperature of the polymer component of the coreparticles is far lower than 80° C., the polymerizable monomer for shellmay be such that forms a polymer having a glass transition temperatureof 80° C. or lower. However, the glass transition temperature of thepolymer formed from the polymerizable monomer for shell must be presetso as to be higher than the glass transition temperature of the polymercomponent of the core particles. In order to improve the shelf stabilityof the resulting polymerized toner, the glass transition temperature ofthe polymer formed from the polymerizable monomer for shell is presetwithin a range of generally 50 to 120° C., preferably 60 to 110° C.,more preferably 80 to 105° C. If the glass transition temperature of thepolymer formed from the polymerizable monomer for shell is extremely toolow, the shelf stability of the resulting polymerized toner may belowered in some cases even if such a glass transition temperature ishigher than that of the polymer component of the core particles. In manycases, the glass transition temperature of the polymer component of thecore particles may be represented by the calculated Tg of a polymerformed from the polymerizable monomer for core.

A difference in glass transition temperature between the polymer formedfrom the polymerizable monomer for core and the polymer formed from thepolymerizable monomer for shell is generally at least 10° C., preferablyat least 20° C., more preferably at least 30° C.

The polymerizable monomer for shell is preferably polymerized in thepresence of the core particles after it is formed into droplets smallerthan the number average particle diameter of the core particles in anaqueous dispersion medium. If the droplet diameter of the droplets ofthe polymerizable monomer for shell is too great, the resultingpolymerized toner shows a tendency to lower its shelf stability. Inorder to form the polymerizable monomer for shell into fine droplets, amixture of the polymerizable monomer for shell and the aqueousdispersion medium is subjected to a finely dispersing treatment by meansof, for example, an ultrasonic emulsifier. It is preferred that theaqueous dispersion thus obtained be added to the aqueous dispersionmedium in which the core particles are present.

The polymerizable monomer for shell is not particularly limited bysolubility in water at 20° C. However, when a polymerizable monomer forshell having a solubility of at least 0.1 wt. % in water at 20° C. isused, the monomer having a high solubility in water at 20° C. becomesliable to quickly migrate to the surfaces of the core particles, so thata polymerized toner having good shelf stability is easy to obtain.

On the other hand, when a polymerizable monomer for shell having asolubility lower than 0.1 wt. % in water at 20° C. is used, itsmigration to the surfaces of the core particles becomes slow. Therefore,it is preferable to polymerize such a monomer after adding it in theform of fine droplets to the reaction system. Even when a polymerizablemonomer for shell having a solubility lower than 0.1 wt. % in water at20° C. is used, the polymerizable monomer for shell becomes easy toquickly migrate to the surfaces of the core particles when an organicsolvent having a solubility of at least 5 wt. % in water at 20° C. isadded to the reaction system, so that a polymerized toner having goodshelf stability is easy to obtain.

Examples of the polymerizable monomer for shell having a solubilitylower than 0.1 wt. % in water at 20° C. include styrene, butyl acrylate,2-ethylhexyl acrylate, ethylene and propylene. Examples of thepolymerizable monomer for shell having a solubility of at least 0.1 wt.% in water at 20° C. include (meth)acrylic esters such as methylmethacrylate and methyl acrylate; amides such as acrylamide andmethacrylamide; vinyl cyanide compounds such as acrylonitrile andmethacrylonitrile; nitrogen-containing vinyl compounds such as4-vinylpyridine; and vinyl acetate and acrolein.

As examples of the organic solvent preferably used in the case where thepolymerizable monomer for shell having a solubility lower than 0.1 wt. %in water at 20° C. is used, may be mentioned lower alcohols such asmethanol, ethanol, isopropyl alcohol, n-propyl alcohol and butylalcohol; ketones such as acetone and methyl ethyl ketone; cyclic etherssuch as tetrahydrofuran and dioxane; ethers such as dimethyl ether anddiethyl ether; and aldehydes such as dimethylformaldehyde.

The organic solvent is added in such an amount that the solubility ofthe polymerizable monomer for shell in the dispersion medium (containingwater and the organic solvent in combination) is at least 0.1 wt. %. Theamount of the organic solvent used varies according to the kind of theorganic solvent, and the kind and amount of the polymerizable monomerfor shell. However, it is generally 0.1 to 50 parts by weight,preferably 0.1 to 40 parts by weight, more preferably 0.1 to 30 parts byweight per 100 parts by weight of the aqueous dispersion medium. Noparticular limitation is imposed on the order of addition of the organicsolvent and the polymerizable monomer for shell to the reaction system.In order to facilitate the migration of the polymerizable monomer forshell to the core particles to make easy to obtain a polymerized tonerhaving good shelf stability, however, it is preferable to first add theorganic solvent to the reaction system and then add the polymerizablemonomer for shell.

When a monomer having a solubility lower than 0.1 wt. % in water at 20°C. and a monomer having a solubility of at least 0.1 wt. % in water at20° C. are used in combination, it is preferable to first add themonomer having a solubility of at least 0.1 wt. % in water at 20° C. topolymerize it, then add the organic solvent, and further add the monomerhaving a solubility lower than 0.1 wt. % in water at 20° C. topolymerize it. According to this adding process, the Tg of the polymerobtained from the polymerizable monomer for shell, which is polymerizedin the presence of the core particles, and the amount of the monomeradded can be suitably controlled for the purpose of controlling thefixing temperature of the resulting polymerized toner.

The polymerizable monomer for shell is preferably used in combinationwith a charge control agent. The charge control agent is used forimproving the charge properties of the resulting polymerized toner. Asthe charge control agent, there may be used various kinds of chargecontrol agents for positive charge and negative charge. As specificexamples of the charge control agents, may be mentioned Nigrosine NO1(product of Orient Chemical Industries Ltd.), Nigrosine EX (product ofOrient Chemical Industries Ltd.), Spiron Black TRH (product of HodogayaChemical Co., Ltd.), T-77 (product of Hodogaya Chemical Co., Ltd.),Bontron S-34 (product of Orient Chemical Industries Ltd.) and BontronE-84 (product of Orient Chemical Industries Ltd.). The charge controlagent is used in a proportion of generally 0.01 to 10 parts by weight,preferably 0.1 to 5 parts by weight per 100 parts by weight of thepolymerizable monomer for shell.

As examples of a specific process for polymerizing the polymerizablemonomer for shell in the presence of the core particles, may bementioned a process in which the polymerizable monomer for shell isadded to the reaction system of the polymerization reaction which hasbeen conducted for obtaining the core particles, thereby continuouslyconducting polymerization, and a process in which the core particlesobtained in a separate reaction system are charged, to which thepolymerizable monomer for shell is added, thereby conductingpolymerization stepwise. The polymerizable monomer for shell may beadded to the reaction system in one lot, or continuously orintermittently by means of a pump such as a plunger pump.

In order to make easy to obtain polymer particles of core-shellstructure, it is preferable to add a water-soluble radical initiator atthe time the polymerizable monomer for shell is added. It is consideredthat when the water-soluble radical initiator is added upon the additionof the polymerizable monomer for shell, the water-soluble initiatorenters in the vicinity of each outer surface of the core particles towhich the polymerizable monomer for shell has migrated, so that apolymer layer (shell) is easy to form on the core particle surface.

As examples of the water-soluble radical initiator, may be mentionedpersulfates such as potassium persulfate and ammonium persulfate; azoinitiators such as 4,4′-azobis-(4-cyanovaleric acid),2,2′-azobis(2-amidinopropane), bihydrochloride and2,2′-azobis-2-methyl-N-1,1′-bis(hydroxymethyl)-2-hydroxyethylpropionamide;and combinations of an oil-soluble initiator such as cumene peroxidewith a redox catalyst. The amount of the water-soluble radical initiatorused is generally 0.001 to 1 wt. % based on the aqueous medium.

(Polymerized toner)

In the polymerized toner according to the present invention, a weightratio of the polymerizable monomer for core to the polymerizable monomerfor shell is generally 40/60 to 99.9/0.1, preferably 60/40 to 99.5/0.5,more preferably 80/20 to 99/1. If the proportion of the polymerizablemonomer for shell is too low, the effect of improving the shelfstability becomes little. If the proportion is too high on the otherhand, the effects of lowering the fixing temperature and improving thepermeability through OHP become little.

The polymerized toner according to the present invention is composed offine spherical particles sharp in particle diameter distribution inwhich the volume average particle diameter is generally 1 to 20 μm,preferably 3 to 15 μm, and the particle diameter distribution (volumeaverage particle diameter/number average particle diameter) is generallyat most 1.6, preferably at most 1.5.

The polymerized toner according to the present invention is composed ofpolymer particles of core-shell structure, comprising the core particlesand the shell which covers each of the core particles.

In the polymerized toner according to the present invention, the averagethickness of the shell is generally 0.001 to 1 μm, preferably 0.005 to0.5 μm. If the thickness of the shell is too great, the fixing abilityof the toner is deteriorated. If the thickness is too small on the otherhand, the shelf stability of the toner is deteriorated. The particlediameters of the core particles and the thickness of the shell in thepolymerized toner can be determined by directly measuring the size andshell thickness of each of particles selected at random from electronphotomicrographs thereof when they can be observed through an electronmicroscope. If the particle diameters of the core particles and thethickness of the shell are difficult to observe through the electronmicroscope, the particle diameters of the core particles are measuredthrough the electron microscope in the same manner as described above orby means of a Coulter counter at the stage of formation of the coreparticles. After the core particles are then covered with the shell, theparticle diameters of the resultant polymerized toner particles aremeasured again through the electron microscope or by means of theCoulter counter, whereby the average thickness of the shell can be foundfrom a change in particle diameter before and after the covering withthe shell. When it is difficult to measure the shell thickness by thesemethods, the thickness of the shell can be calculated out from theparticle diameter of the core particles and the used amount of thepolymerizable monomer for forming the shell.

The polymerized toner according to the present invention containstoluene-insoluble matter in an amount of generally at most 50 wt. %,preferably at most 20 wt. %, more preferably at most 10 wt. %. If thetoluene-insoluble matter is contained in plenty, such a polymerizedtoner shows a tendency to lower its fixing ability. Thetoluene-insoluble matter is determined by placing a polymer massobtained by pressing the polymerized toner in a 80-mesh woven metalbasket, immersing the basket in toluene for 24 hours at roomtemperature, and then measuring the dry weight of solids remaining inthe basket to express it in terms of % by weight based on the weight ofthe polymer.

The polymerized toner according to the present invention has a ratio(rl/rs) of the length (rl) to the breadth (rs) within a range of 1 to1.25, preferably 1 to 1.20, more preferably 1 to 1.15. If the ratio istoo high, the resolution of an image formed from such a polymerizedtoner is deteriorated. In addition, when such a polymerized toner iscontained in a toner container in an image forming apparatus, itsdurability shows a tendency to lower, since friction between particlesof the polymerized toner becomes greater, and so external additives areseparated from the toner.

(Developer)

The polymerized toner according to the present invention may be used asa developer as it is. However, it is generally combined with externaladditives such as a flowability improver and an abrasive to provide adeveloper. When the external additives are added and mixed into thepolymerized toner, the additives attach to the surface of thepolymerized toner. The external additives bear an action that theflowability of the polymerized toner is enhanced, or that the formationof a toner film on a photosensitive member or the like is prevented bytheir abrading action.

Typical external additives include inorganic particles and organic resinparticles. Examples of the inorganic particles include particles ofsilica, aluminum oxide, titanium oxide, zinc oxide, tin oxide, bariumtitanate, strontium titanate, etc. Examples of the organic resinparticles include particles of methacrylic ester polymers, acrylic esterpolymers, styrene-methacrylic ester copolymers and styrene-acrylic estercopolymers, and core-shell type particles in which the core is composedof a methacrylic ester polymer, and the shell is composed of a styrenepolymer.

Of these, the particles of the inorganic oxides are preferred, and thesilica particles are more preferred, with silica particles subjected toa hydrophobicity-imparting treatment being particularly preferred. Inorder to attach the external additives to the polymerized toner, ingeneral, the external additives and the polymerized toner are chargedinto a mixer such as a Henschel mixer to mix them under stirring. Noparticular limitation is imposed of the amount of the external additivesused. However, it is generally about 0.1 to 6 parts by weight per 100parts by weight of the polymerized toner.

When the polymerized toner according to the present invention is used,the fixing temperature can be lowered to a low temperature of 80 to 180°C., preferably 100 to 150° C., more preferably 100 to 130° C. Inaddition, the polymerized toner does not aggregate during its storageand is hence excellent in shelf stability.

(Image forming apparatus)

An image forming apparatus, to which the polymerized toner according tothe present invention is applied, comprises a photosensitive member(photosensitive drum), a means for charging the surface of thephotosensitive member, a means for forming an electrostatic latent imageon the surface of the photosensitive member, a means for receiving atoner (developer), a means for supplying the toner to develop theelectrostatic latent image on the surface of the photosensitive member,thereby forming a toner image, and a means for transferring the tonerimage from the surface of the photosensitive member to a transfermedium. A specific example of such an image forming apparatus isillustrated in FIG. 1.

As illustrated in FIG. 1, in the image forming apparatus, aphotosensitive drum 1 as a photosensitive member is installed rotatablyin the direction of an arrow A. The photosensitive drum 1 has astructure that a photoconductive layer is provided around a peripheralsurface of an electroconductive support drum. The photoconductive layeris composed of, for example, an organic photosensitive member, seleniumphotosensitive member, zinc oxide photosensitive member or amorphoussilicon photosensitive member.

Around the photosensitive drum 1, a charging roll 2 as a charging means,a laser beam irradiating device 3 as a latent image forming means, adeveloping roll 4 as a developing means, a transfer roll 10 as atransfer means, and optionally a cleaning device (not illustrated) arearranged along the circumferential direction of the drum.

The charging roll 2 serves to uniformly and evenly charge the surface ofthe photosensitive drum 1 either positively or negatively. Voltage isapplied to the charging roll 2, and the charging roll 2 is brought intocontact with the surface of the photosensitive drum 1, thereby chargingthe surface of the photosensitive drum 1. The charging roller 2 may bereplaced by a charging means according to corona discharge.

The laser beam irradiating device 3 serves to irradiate the surface ofthe photosensitive drum 1 with light corresponding to image signals toexpose the surface of the photosensitive drum 1 evenly charged to thelight on the predetermined pattern, thereby forming an electrostaticlatent image on the exposed portion of the drum (in the case of reversaldevelopment) or forming an electrostatic latent image on the unexposedportion of the drum (in the case of normal development). An example ofother latent image forming means includes that composed of an LED arrayand an optical system.

The developing roll 4 serves to apply a toner to the electrostaticlatent image formed on the photosensitive drum 1. Bias voltage isapplied between the developing roll 4 and the photosensitive drum 1 insuch a manner that the toner is applied only to a light-exposed portionof the photosensitive drum 1 in reversal development, or only to alight-unexposed portion of the photosensitive drum 1 in normaldevelopment.

In a casing 9 for receiving the toner 7, the developing roll 4 and afeed roll 6 are provided. The developing roll 4 is arranged in closevicinity to the photosensitive drum 1 in such a manner that a partthereof comes into contact with the photosensitive drum 1, and isrotated in a direction B opposite to the rotating direction of thephotosensitive drum 1. The feed roll 6 is rotated in contact with and inthe same direction C as the developing roll 4 to supply the toner 7 tothe outer periphery of the developing roll 4. An agitating means(agitating blade) 8 for agitating the toner is installed in the casing9.

A blade 5 for developing roll as a layer thickness regulating means isarranged at a position between the contact point with the feed roll 6and the contact point with the photosensitive drum 1 on the periphery ofthe developing roll 4. The blade 5 is composed of conductive rubber orstainless steel, and voltage of |200 V| to |600 V| is applied to theblade to charge the toner. Therefore, the resistivity of the blade 5 ispreferably 10⁶ Ωcm or lower.

The polymerized toner 7 according to the present invention is containedin the casing 9 of the image forming apparatus. The polymerized toner 7may comprise external additives such as a flowability improver. Sincethe polymerized toner according to the present invention has acore-shell structure, and the shell of the surface layer is formed of apolymer having a relatively high glass transition temperature, thestickiness of the surface is reduced, and so the polymerized toner isprevented from aggregating during storage in the casing 9. In addition,since the particle diameter distribution of the polymerized toneraccording to the present invention is relatively sharp, the toner layerformed on the developing roll 4 can be made a substantially single layerby the layer thickness regulating means 5, thereby forming images withgood reproducibility.

The transfer roll 10 serves to transfer the toner image formed on thesurface of the photosensitive drum 1 by the developing roll 4 to atransfer medium 11. Examples of the transfer medium 11 include paper andresin sheets such as OHP sheets. As transferring means, may be mentioneda corona discharge device and a transfer belt in addition to thetransfer roll 10.

The toner image transferred to the transfer medium 11 is fixed to thetransfer medium by a fixing means. The fixing means is generallycomposed of a heating means and a press-bonding means. Morespecifically, the fixing means is generally composed of the combinationof a heating roll (fixing roll) 12 and a press roll 13. The transfermedium 11, to which the toner image has been transferred, is passedthrough between the heating roll 12 and the press roll 13 to melt thetoner, and at the same time press-bond it to the transfer medium 11,thereby fixing the toner image thereto.

In the image forming apparatus. according to the present invention, thepolymerized toner according to the present invention is used as a toner.Therefore, the toner is easily melted even when the heating temperatureby the heating means is low, and is fixed to the surface of the transfermedium in a flattened state by slightly pressing it by the press-bondingmeans, so that high-speed printing or copying is feasible. Further, thetoner image fixed to an OHP sheet is excellent in permeability throughOHP.

The cleaning device serves to clean off the toner remaining on thesurface of the photosensitive drum 1 without transferring and iscomposed of, for example, a cleaning blade or the like. The cleaningdevice is not always required to install in the case where a system thatcleaning is conducted by the developing roll 4 at the same time asdevelopment is adopted.

The image forming apparatus illustrated in FIG. 1 comprises, for onephotosensitive member, each one of the means for charging the surface ofthe photosensitive member, the means for forming an electrostatic latentimage on the surface of the photosensitive member, the means forreceiving the polymerized toner, the means for supplying the polymerizedtoner to develop the electrostatic latent image on the surface of thephotosensitive member, thereby forming a toner image, and the means fortransferring the toner image from the surface of the photosensitivemember to a transfer medium. However, the image forming apparatusaccording to the present invention includes a full-color image formingapparatus for forming full-color images, comprising a photosensitivemember, and around the photosensitive member, at least four means forrespectively forming electrostatic latent images corresponding tomagenta, yellow, blue and black on the surface of the photosensitivemember, at least four means for respectively receiving the polymerizedtoners corresponding to magenta, yellow, blue and black, and at leastfour means for respectively supplying the polymerized toners to developtheir corresponding electrostatic latent images on the surface of thephotosensitive member, thereby forming a toner image.

(Image forming process)

In the image forming process making use of the polymerized tonersaccording to the present invention, which comprises the steps ofapplying a toner to the surface of a photosensitive member, on which anelectrostatic latent image has been formed, to make the latent imagevisible, and then transferring the visible image to a transfer medium,the polymerized toner according to the present invention is used as thetoner.

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples. Incidentally, alldesignations of “part” or “parts” and “%” as will be used in thefollowing examples mean part or parts by weight and wt. % unlessexpressly noted.

Physical properties in the following Examples and Comparative Exampleswere measured in accordance with the following respective methods.

(1) Particle Diameter of Toner:

The volume average particle diameter (dv) and particle diameterdistribution, i.e., a ratio (dv/dp) of the volume average particlediameter to a number average particle diameter (dp) of a polymerizedtoner sample were measured by means of a Multisizer (manufactured byCoulter Co.). The measurement by the Multisizer was conducted under thefollowing conditions:

aperture diameter: 50 μm;

medium: Isothone II, concentration: 10%; and

number of particles measured: 50,000 particles.

(2) Thickness of Shell:

In the examples of the present invention, the thickness of shell in eachtoner sample was calculated out in the following equation, since thethickness of the shell was thin though it can be measured by theMultisizer or through an electron microscope where the thickness of theshell is great.

π(r+x)³/πr³=1+s/100ρ  (i)

wherein

r: the radius of core particles before addition of a polymerizablemonomer for shell (a half of the volume average particle diameter of thecore particles found from measurement by the Multisizer; μm);

x: the thickness (μm) of shell;

s: the number of parts of the polymerizable monomer for shell added (thenumber of parts per 100 parts by weight of a polymerizable monomer forcore); and

ρ: the density (g/cm³) of a polymer forming the shell.

The equation (i) is transformed into the equation (ii):

(x+r)/r=(1+s/100ρ)^(⅓)  (ii)

When ρ=1 is substituted into the equation (ii), the equation (iii) isobtained.

(x+r)/r=(1+s/100)^(⅓)  (iii)

From the equation (iii), the equation (iv) is derived.

x=r(1+s/100)^(⅓)−r  (iv)

The thickness of the shell was calculated out using the equation (iv).

(3) Volume Resistivity of Toner:

The volume resistivity of each toner sample was measured by means of adielectric loss measuring device (TRS-10 Model, trade name; manufacturedby Ando Electric Co., Ltd.) under conditions of a temperature of 30° C.and a frequency of 1 kHz.

(4) Fixing Temperature of Toner:

A commercially available printer of a non-magnetic one-componentdevelopment system was modified in such a manner that the temperature ofa fixing roll can be varied. This modified printer was used to evaluatea toner sample as to the image. A temperature at which a fixing rate ofthe toner amounted to 80% was defined as a fixing temperature. Thefixing test was conducted by varying the temperature of the fixing rollin the printer to determine the fixing rate at each temperature, therebyfinding a relationship between the temperature and the fixing rate. Thefixing rate was calculated from the ratio of image densities before andafter a peeling operation using a pressure-sensitive adhesive tape,which was conducted against a black solid-printed area of a test papersheet, on which printing had been made by the modified printer. Morespecifically, assuming that the image density before the peeling of theadhesive tape is ID_(before), and the image density after the peeling ofthe adhesive tape is ID_(after), the fixing rate is determined by thefollowing equation:

Fixing rate (%)=(ID_(after)/ID_(before))×100

The peeling operation of the pressure-sensitive adhesive tape is aseries of operation that a pressure-sensitive adhesive tape (ScotchMending Tape 810-3-18, product of Sumitomo 3M Limited) is applied to ameasuring area of the test paper sheet to cause the tape to adhere tothe sheet by pressing the tape under a fixed pressure, and the adhesivetape is then peeled at a fixed rate in a direction along the papersheet. The image density was measured by means of a reflection imagedensitometer manufactured by McBeth Co.

(5) Shelf Stability of Toner:

The evaluation of shelf stability was conducted by placing each tonersample in a closed container to seal it, sinking the container into aconstant-temperature water bath controlled to 55° C. and then taking thecontainer out of the water bath after a predetermined period of timewent on, thereby measuring the weight of toner aggregated. The sampletoner taken out of the container was transferred to a 42-mesh screen soas not to destroy the structure thereof as much as possible, and thescreen was vibrated for 30 seconds by means of a powder measuringdevice, REOSTAT (manufactured by Hosokawa Micron Corporation) with theintensity of vibration preset to 4.5. Thereafter, the weight of thetoner remaining on the screen was measured to regard it as the weight ofthe toner aggregated. The aggregation rate (wt. %) of the toner wascalculated out from this weight of the aggregated toner and the weightof the sample. The shelf stability of the toner sample was evaluated by4 ranks in accordance with the following standard:

⊚: aggregation rate was lower than 5 wt. %;

∘: aggregation rate was not lower than 5 wt. %, but low than 10 wt. %;

Δ: aggregation rate was not lower than 10 wt. %, but low than 50 wt. %;and

X: aggregation rate was not lower than 50 wt. %.

(6) Permeability through OHP:

The temperature of the fixing roll in the modified printer describedabove was preset to 170° C. to conduct printing with each toner sampleon a commercially available OHP sheet (Transparency, product of UchidaYoko Co., Ltd.), thereby evaluating the toner sample as to permeabilitythrough OHP. The printed OHP sheet was set in an OHP to visually observewhether the color of the printed image was projected or not, therebyranking it in accordance with the following standard:

∘: Good in permeability;

Δ: Insufficient in permeability; and

X: The image did not permeate.

(7) Charge Level of Toner:

The charge level of each toner sample was measured under respectiveenvironments of L/L (10° C. in temperature and 20% in humidity) and H/H(35° C. in temperature and 80% in humidity) to evaluate the toner sampleas to charge level under varied environments.

The charge level of the toner was determined in the following manner.The toner was charged into a commercially available printer (4 papersper minute printer) under each of the above-described environments andleft to stand for 24 hours. Thereafter, a print pattern of half tone wasprinted 5 times, and the toner on a developing roll was then sucked in asuction type charge level meter to measure a charge level per unitweight from the charge level and weight of the toner sucked at thistime.

(8) Evaluation of Image:

Printing was continuously conducted with each toner sample from thebeginning to count the number of printed sheets that continuouslyretained an image density of 1.3 or higher as measured by a reflectiondensitometer (manufactured by McBeth Co) and at an unprinted area, fogof 10% or lower as measured by a whiteness meter (manufactured by NipponDenshoku K.K.), thereby evaluating the toner sample as to image inaccordance with the following standard:

∘: the number of the printed sheets that continuously retained theabove-described image quality was 10,000 or more;

Δ: the number of the printed sheets that continuously retained theabove-described image quality was not less than 5,000, but less than10,000; and

X: the number of the printed sheets that continuously retained theabove-described image quality was less than 5,000.

Referential Example 1

In 500 parts of benzene, were dissolved 100 parts of an unsaturatedpolyester (softening point: 120° C., acid value: 8), and the resultantsolution was charged into a vessel equipped with a stirrer, an internalheater, a condenser and a liquid-solid feed opening, and heated to 60°C. with stirring. Each 0.1 mol of benzylidenestearylamine, benzoylchloride and tin tetrachloride were then added from the feed opening toconduct a reaction for about 1 hour. After completion of the reaction,the reaction mixture was poured into 1,000 cm³ of methanol to solidify areaction product. The thus-obtained solidified product was left to standin a vacuum drier to dry it, thereby obtaining a compound (S1/S2=2.2)having a bond represented by the formula (1). The amount of the bondrepresented by the formula (1) to be present was determined by a ratioof the intensity (S1) of ultraviolet absorption at 315 nm to intensity(S2) by a refractometer, measured by gel permeation chromatography(GPC).

Referential Example 2

A compound (S1/S2=2.9) having a bond represented by the formula (1) wasobtained in the same manner as in Referential Example 1 except that theunsaturated polyester used in Referential Example 1 was changed to astyrene-butadiene block copolymer (styrene/butadiene=90/10, weightaverage molecular weight: 20,000), and benzylidenestearylamine, benzoylchloride and tin tetrachloride were changed to benzylidenebutylamine,acetyl chloride and titanium tetrachloride, respectively.

Referential Example 3

A compound (S1/S2=3.0) having a bond represented by the formula (1) wasobtained in the same manner as in Referential Example 1 except that theunsaturated polyester used in Referential Example 1 was changed to astyrene-butadiene random copolymer (styrene/butadiene=90/10, weightaverage molecular weight: 50,000).

Example 1

A monomer mixture (calculated Tg of the resulting copolymer=50° C.)composed of 78 parts of styrene and 22 parts of n-butyl acrylate, 7parts of carbon black (Printex 150T, trade name; product of Degussa AG),2 parts of the compound obtained in Referential Example 1, 1 part of acharge control agent (Spiron Black TRH, trade name; product of HodogayaChemical Co., Ltd.), 0.3 parts of divinylbenzene, 0.5 parts of apolymethacrylic ester macromonomer (AA6; Tg=94° C.; product of ToagoseiChemical Industry Co., Ltd.), and 10 parts of pentaerythritoltetrastearate were dispersed in a ball mill at room temperature toobtain a stock dispersion.

On one hand, 10 parts of methyl methacrylate (calculated Tg of theresulting polymer=105° C.), 100 parts of water and 0.01 parts of acharge control agent (Bontron E-84, product of Orient ChemicalIndustries Ltd.) were subjected to a finely dispersing treatment by anultrasonic emulsifier, thereby obtaining an aqueous dispersion of apolymerizable monomer for shell. The droplet diameter of droplets of thepolymerizable monomer for shell was found to be 1.6 μm in terms of D₉₀as determined by means of a microtrack particle diameter distributionmeasuring device by adding the droplets at a concentration of 3% to a 1%aqueous solution of sodium hexametaphosphate.

On the other hand, an aqueous solution with 6.9 parts of sodiumhydroxide (alkali metal hydroxide) dissolved in 50 parts ofion-exchanged water was gradually added to an aqueous solution with 9.8parts of magnesium chloride (water-soluble polyvalent metallic salt)dissolved in 250 parts of ion-exchanged water under stirring to preparea dispersion of colloid of magnesium hydroxide (colloid of hardlywater-soluble metal hydroxide). The particle diameter distribution ofthe colloid formed was measured by means of the microtrack particlediameter distribution measuring device (manufactured by Nikkiso Co.,Ltd.) and found to be 0.38 μm in terms of D₅₀ (50% cumulative value ofnumber particle diameter distribution) and 0.82 μm in terms of D₉₀ (90%cumulative value of number particle diameter distribution). Themeasurement by means of the microtrack particle diameter distributionmeasuring device was performed under the following conditions:

measuring range: 0.12 to 704 μm;

measuring time: 30 seconds; and

medium: ion-exchanged water.

The stock dispersion prepared above was poured into the colloidaldispersion of magnesium hydroxide obtained above, and 4 parts of t-butylperoxy-2-ethylhexanoate were added with stirring to prepare apolymerizable monomer composition for core. The resultant monomercomposition was stirred at 12,000 rpm under high shearing force by meansof a TK type homomixer to form droplets of the polymerizable monomercomposition for core. The thus-prepared aqueous dispersion containingdroplets of the polymerizable monomer composition for core was chargedinto a reactor equipped with an agitating blade to initiate apolymerization reaction at 90° C. At the time a conversion into apolymer reached 98%, the polymerizable monomer for shell prepared aboveand 1 part of a 1% aqueous solution of potassium persulfate were addedto continue the reaction for 3 hours. Thereafter, the reaction wasstopped to obtain an aqueous dispersion containing polymer particles ofcore-shell structure.

The volume average particle diameter (dv) of core particles as measuredby taking out them just before the addition of the polymerizable monomerfor shell was 6.2 μm, and a ratio of the volume average particlediameter (dv) to the number average particle diameter (dp) thereof was1.24. The resultant polymer particles had a shell thickness of 0.31 μmas calculated out from the used amount of the polymerizable monomer forshell and the particle diameter of the core particle, and an rl/rs ratioof 1.1 and contained 3% of toluene-insoluble matter.

While stirring the above-obtained aqueous dispersion of the polymerparticles of core-shell structure, the pH of the system was adjusted tonot higher than 4 with sulfuric acid to conduct acid washing (25° C., 10minutes). After water was separated by filtration from the dispersion,500 parts of ion-exchanged water were newly added to form a slurryagain, and the slurry was washed with water. Thereafter, the dehydrationand water washing were repeated several times, and solids were thencollected by filtration. The thus-collected solids were dried at 45° C.for 2 days by a dryer to obtain polymer particles (polymerized toner).

To 100 parts of the polymerized toner obtained above were added 0.3parts of colloidal silica (R-202, trade name; product of Nippon AerosilCo., Ltd.) subjected to a hydrophobicity-imparting treatment, and theywere mixed by means of a Henschel mixer to prepare a developer(hereinafter referred to as “toner” merely). The volume resistivity ofthe toner thus obtained was measured and found to be 11.3 (logΩ·cm).

The toner thus obtained was used to measure its fixing temperature. As aresult, it was 120° C. The shelf stability of the toner was extremelygood (rank=⊚). The results are shown in Table 1. Besides, the evaluationof image revealed that an image high in image density, free of fog andirregularities, and extremely good in resolution was obtained (rank=∘).

Example 2

A polymerized toner was obtained in the same manner as in Example 1except that the compound obtained in Referential Example 1 used inExample 1 was changed to the compound obtained in Referential Example 2.The results are shown in Table 1.

Comparative Example 1

A polymerized toner was obtained in the same manner as in Example 1except that the styrene-butadiene block copolymer (ST/BD=9/1; Mw=20,000)used in Referential Example 2 was used in place of the compound obtainedin Referential Example 1 used in Example 1. The results are shown inTable 1.

Comparative Example 2

A polymerized toner was obtained in the same manner as in Example 1except that the unsaturated polyester (softening point: 120° C., acidvalue: 8) used in Referential Example 2 was used in place of thecompound obtained in Referential Example 1 used in Example 1. Theresults are shown in Table 1.

Example 3

A polymerized toner was obtained in the same manner as in Example 1except that 10 parts of methyl methacrylate used in the polymerizablemonomer composition for shell in Example 1 were changed to 9 parts ofmethyl methacrylate and 1 part of butyl acrylate, and the compoundobtained in Referential Example 1 was changed to the compound obtainedin Referential Example 3. The results are shown in Table 1.

TABLE 1 Example Comp. Ex. 1 2 3 1 2 Core particles: dv [μm] 6.2 6.5 6.48.3 7.8 dv/dp 1.24 1.27 1.25 1.52 1.62 Polymer particles: Thickness ofshell [μm] 0.31 0.32 0.32 0.41 0.39 Toluene-insoluble 3 4 3 4 7 matter[%] Evaluation of toner: dv [μm] 6.8 7.1 7.0 9.1 8.6 dv/dp 1.26 1.301.28 1.57 1.68 Volume resistivity 11.3 11.4 11.4 10.8 10.6 [logΩcm]Fixing temperature [° C.] 120 130 120 140 140 Shelf stability ⊚ ⊚ ⊚ Δ ΔCharge level under −31 −30 −29 −19 −16 L/L [μc/g] Charge level under −30−29 −28 −11 −9 H/H [μc/g] Evaluation of image ◯ ◯ ◯ × ×

As apparent from the result shown in Table 1, when the polymerizedtoners (Examples 1 to 3) according to the present invention are used,the fixing temperature thereof can be lowered to 120 to 130° C. Inaddition, the polymerized toners are excellent in shelf stability, lowin the dependence of charge level on environment, and hard to causefogging, lowering of image density, etc. On the other hand, thepolymerized toners according to Comparative Examples 1 and 2 areinsufficient in the balance between the effect of lowering the fixingtemperature and the shelf stability, high in the dependence of chargelevel on environment, and also low in the evaluation of image.

Example 4

A polymerized toner was obtained in the same manner as in Example 1except that styrene was used in place of methyl methacrylate making upthe polymerizable monomer composition for shell in Example 1, and 20parts of methanol were added to the reaction system right before theaddition of the polymerizable monomer composition for shell. The resultsare shown in Table 2.

Example 5

A polymerized toner was obtained in the same manner as in Example 1except that 2,2-azobisisobutyronitrile was used in place of t-butylperoxy-2-ethylhexanoate used as the polymerization initiator for thepolymerizable monomer for core in Example 1, and the reactiontemperature was changed to 75° C. The results are shown in Table 2. Whena developer (toner) containing this polymerized toner was used toconduct fixing, slight odor was given off.

Example 6

A polymerized toner was obtained in the same manner as in Example 1except that the compound obtained in Referential Example 1 used inExample 1 was changed to the compound obtained in Referential Example 3.The results are shown in Table 2.

Example 7

A polymerized toner was obtained in the same manner as in Example 1except that butyl acrylate used in the polymerizable monomer compositionfor core in Example 1 was changed to 2-ethylhexyl acrylate. The resultsare shown in Table 2.

TABLE 2 Example 4 5 6 7 Core particles: dv [μm] 6.4 6.5 6.4 6.5 dv/dp1.21 1.28 1.21 1.25 Polymer particles: Thickness of shell [μm] 0.32 0.320.32 0.32 Toluene-insoluble matter [%] 3 4 4 5 Evaluation of toner: dv[μm] 7.0 7.1 7.0 7.1 dv/dp 1.24 1.30 1.23 1.26 Volume resistivity[logΩcm] 11.3 11.4 11.4 11.5 Fixing temperature [° C.] 120 130 120 130Shelf stability ⊚ ⊚ ⊚ ⊚ Charge level under L/L [μc/g] −29 −29 −30 −28Charge level under H/H [μc/g] −28 −28 −29 −27 Evaluation of image ◯ ◯ ◯◯

As apparent from the result shown in Table 2, when the polymerizedtoners (Examples 4 to 7) according to the present invention are used,the fixing temperature thereof can be lowered to 120 to 130° C. Inaddition, the polymerized toners are excellent in shelf stability, lowin the dependence of charge level on environment, and hard to causefogging, lowering of image density, etc.

Example 8

A polymerized toner was obtained in the same manner as in Example 1except that 5 parts of a magenta pigment (Pigment Red 122) were used inplace of 7 parts of carbon black used in Example 1. The results areshown in Table 3.

Example 9

A polymerized toner was obtained in the same manner as in Example 1except that 5 parts of a yellow quinophthalone pigment (Pigment Yellow138) were used in place of 7 parts of carbon black used in Example 1.The results are shown in Table 3.

Example 10

A polymerized toner was obtained in the same manner as in Example 1except that 5 parts of a cyan pigment (Pigment Blue 15:3) were used inplace of 7 parts of carbon black used in Example 1. The results areshown in Table 3.

Comparative Example 3

A polymerized toner was obtained in the same manner as in ComparativeExample 1 except that 5 parts of a magenta pigment (Pigment Red 122)were used in place of 7 parts of carbon black used in ComparativeExample 1. The results are shown in Table 3.

TABLE 3 Comp. Example Ex. 8 9 10 3 Core particles: dv [μm] 6.3 6.6 6.88.8 dv/dp 1.23 1.17 1.26 1.68 Polymer particles: Thickness of shell [μm]0.31 0.33 0.34 0.43 Toluene-insoluble matter [%] 5 4 5 4 Evaluation oftoner: dv [μm] 6.9 7.3 7.5 9.7 dv/dp 1.25 1.20 1.28 1.70 Volumeresistivity [logΩcm] 11.8 11.9 11.6 10.7 Fixing temperature [° C.] 120130 120 140 Shelf stability ⊚ ⊚ ⊚ Δ Charge level under L/L [μc/g] −31−30 −29 −16 Charge level under H/H [μc/g] −30 −29 −28 −8 Permeabilitythrough OHP ◯ ◯ ◯ Δ Evaluation of image ◯ ◯ ◯ ×

As apparent from the result shown in Table 3, when the polymerizedtoners (Examples 8 to 10) according to the present invention are used,the fixing temperature thereof can be lowered to 120 to 130° C. Inaddition, the polymerized toners are excellent in shelf stability, lowin the dependence of charge level on environment, and hard to causefogging, lowering of image density, etc. Further, the polymerized tonersaccording to the present invention is excellent in permeability throughOHP. On the other hand, the polymerized toner according to ComparativeExample 3 is insufficient in the balance between the effect of loweringthe fixing temperature and the shelf stability, high in the dependenceof charge level on environment, and also low in the evaluation of image.

INDUSTRIAL APPLICABILITY

According to the present invention, there are provided polymerizedtoners which have a low fixing temperature and uniformly meltingability, and moreover are excellent in shelf stability, and a productionprocess thereof. The use of the polymerized toners according to thepresent invention permits the speeding-up of copying or printing, theformation of full-color images and energy saving. The polymerized tonersaccording to the present invention can form toner images which exhibitexcellent permeability when conducting printing on an OHP sheet withsuch a polymerized toner and fixing the resulting image thereto. Thepolymerized toners according to the present invention permit theformation of high-quality images without causing fogging and lowering ofimage density. According to the present invention, there are provided animage forming process comprising using the polymerized toner(s) havingsuch excellent various properties, and an image forming apparatus inwhich the polymerized toner(s) are received.

What is claimed is:
 1. A polymerized toner of core-shell structure,comprising core particles composed of colored polymer particles whichcontain a compound having at least one >C═N⁺< structure in its moleculeand a colorant, and a layer of a polymer having a glass transitiontemperature higher than that of a polymer component making up the coreparticles, said polymer layer covering each of the core particles. 2.The polymerized toner according to claim 1, wherein the compound havingat least one >C═N⁺< structure in its molecule is aheterocycle-containing compound.
 3. The polymerized toner according toclaim 2, wherein the heterocycle-containing compound is (i) a compoundhaving the structure of a 1,3-oxazine ring or 4H,5H-1,3-oxazine ring, inwhich the nitrogen atom in the oxazine ring has been converted into aquaternary ammonium salt, (ii) a compound having a 1,3-thiazine ring or5H,6H-1,3-thiazine ring, in which the nitrogen atom in the thiazine ringhas been converted into a quaternary ammonium salt, (iii) a compoundhaving an isoxazole ring or 4H,5H-isoxazole ring, in which the nitrogenatom in the isoxazole ring has been converted into a quaternary ammoniumsalt, (iv) a compound having a 1,2-diazole ring or 4H,5H-1,3-1,2-diazolering, in which the nitrogen atom in the diazole ring has been convertedinto a quaternary ammonium salt, or (v) a compound having a 2H-pyrrolering or 2H,3H,4H-pyrrole ring, in which the nitrogen atom in the pyrrolering has been converted into a quaternary ammonium salt.
 4. Thepolymerized toner according to claim 1, wherein the compound having atleast one >C═N⁺< structure in its molecule is a modified polymersobtained by reacting an organic compound having a —C(═Y)—N< bond, inwhich Y is an oxygen atom or sulfur atom, with a living anionic polymerobtained by polymerizing a monomer using an alkali metal or alkalineearth metal, and having an ion of such a metal at its terminal, or ametal-added polymer obtained by reacting an unsaturated polymer havingdouble bonds in its polymer chain or side chain with an alkali metal oralkaline earth metal, and then hydrolyzing the reaction product; or ahydrogenated modified polymer obtained by hydrogenating double bonds inthe modified polymer thus obtained.
 5. The polymerized toner accordingto claim 1, wherein the core particles contains the compound having atleast one >C═N⁺< structure in its molecule in a proportion of 0.05 to300 parts by weight per 100 parts by weight of the colorant.
 6. Thepolymerized toner according to claim 1, wherein the core particles arecolored polymer particles obtained by subjecting a polymerizable monomercomposition containing the compound having at least one >C═N⁺< structurein its molecule, the colorant and a polymerizable monomer for core tosuspension polymerization.
 7. The polymerized toner according to claim6, wherein the polymerizable monomer composition further comprises amacromonomer.
 8. The polymerized toner according to claim 6, wherein thepolymerizable monomer composition further comprises a crosslinkingmonomer.
 9. The polymerized toner according to claim 1, wherein theshell is a polymer layer formed by subjecting a polymerizable monomerfor shell to suspension polymerization in the presence of the coreparticles.
 10. The polymerized toner according to claim 1, wherein thecore particles further contain a parting agent.
 11. The polymerizedtoner according to claim 1, wherein the core particles having a volumeaverage particle diameter (dv) of 1 to 20 μm and a ratio of the volumeaverage particle diameter (dv) to a number average particle diameter(dp) of at most 1.7 are covered with the shell composed of the polymerlayer having an average thickness of 0.001 to 1.0 μm.
 12. A process forproducing a polymerized toner of core-shell structure, which comprisesthe steps of (I) polymerizing a polymerizable monomer compositioncontaining a compound having at least one >C═N⁺< structure in itsmolecule, a colorant and a polymerizable monomer for core to preparecore particles formed of colored polymer particles; and then (II)polymerizing a polymerizable monomer for shell, which is capable offorming a polymer having a glass transition temperature higher than thatof a polymer component making up the core particles, in the presence ofthe core particles in an aqueous dispersion medium to form shell whichis formed of a polymer layer and covers each of the core particles. 13.The production process according to claim 12, wherein in the steps (I)and (II), the suspension polymerization is conducted in an aqueousdispersion medium containing a dispersing agent.
 14. The productionprocess according to claim 13, wherein colloid of a hardly water-solublemetal hydroxide is used as the dispersing agent.
 15. The productionprocess according to claim 14, wherein the colloid of the hardlywater-soluble metal hydroxide is such that the 50% cumulative value(D₅₀) of number particle diameter distribution thereof is at most 0.5μm, and the 90% cumulative value (D₉₀) of number particle diameterdistribution thereof is at most 1 μm.
 16. The production processaccording to claim 14, wherein the colloid of the hardly water-solublemetal hydroxide is obtained by adjusting the pH of an aqueous solutionof a water-soluble polyvalent metallic compound to 7 or higher.
 17. Theproduction process according to claim 12, wherein the polymerizablemonomer for core comprises a styrenic monomer and a (meth)acrylic acidderivative.
 18. The production process according to claim 12, wherein inthe step (I), the polymerizable monomer composition further comprises amacromonomer.
 19. The production process according to claim 18, whereinthe macromonomer is contained in an amount of 0.01 to 10 parts by weightper 100 parts by weight of the polymerizable monomer for core.
 20. Theproduction process according to claim 12, wherein in the step (I), thepolymerizable monomer composition further comprises a crosslinkingmonomer.
 21. The production process according to claim 12, wherein inthe step (I), the polymerizable monomer composition further comprises aparting agent.
 22. The production process according to claim 12, whereinin the step (I), the polymerizable monomer composition contains thecompound having at least one >C═N⁺< structure in its molecule in aproportion of 0.05 to 300 parts by weight per 100 parts by weight of thecolorant.
 23. The production process according to claim 13, wherein inthe step (I), the polymerizable monomer composition is poured into theaqueous dispersion medium containing the dispersing agent to form minutedroplets of the polymerizable monomer composition under stirring, andthe suspension polymerization is then conducted in the presence of anoil-soluble radical polymerization initiator at a temperature of 30 to200° C., thereby preparing core particles composed of colored polymerparticles.
 24. The production process according to claim 23, wherein inthe step (I), core particles composed of colored polymer particleshaving a volume average particle diameter (dv) of 1 to 20 μm and a ratioof the volume average particle diameter (dv) to a number averageparticle diameter (dp) of at most 1.7 are prepared.
 25. The productionprocess according to claim 13, wherein in the step (II), thepolymerizable monomer for shell is prepared into droplets having anumber average droplet diameter smaller than the core particles and thensubjected to the suspension polymerization.
 26. The production processaccording to claim 13, wherein in the step (II), a polymerizable monomerfor shell having a solubility lower than 0.1 wt. % in water at 20° C.and an organic solvent having a solubility of at least 5 wt. % in waterat 20° C. are added to conduct the suspension polymerization.
 27. Theproduction process according to claim 13, wherein in the step (II), thepolymerizable monomer for shell and a charge control agent are added toconduct the suspension polymerization.
 28. The production processaccording to claim 13, wherein in the step (II), the polymerizablemonomer for shell is subjected to the suspension polymerization using awater-soluble radical polymerization initiator.
 29. The productionprocess according to claim 12, wherein in the step (II), shell formed ofa polymer layer having an average film thickness of 0.001 to 1.0 μm isformed.
 30. An image forming process, comprising the steps of applying atoner to the surface of a photosensitive member, on which anelectrostatic latent image has been formed, to make the latent imagevisible, and then transferring the visible image to a transfer medium,wherein a polymerized toner of core-shell structure, comprising coreparticles composed of colored polymer particles which contain a compoundhaving at least one >C═N⁺< structure in its molecule and a colorant, anda layer of a polymer having a glass transition temperature higher thanthat of a polymer component making up the core particles, said polymerlayer covering each of the core particles, is used as the toner.
 31. Animage forming apparatus, comprising a photosensitive member, a means forcharging the surface of the photosensitive member, a means for formingan electrostatic latent image on the surface of the photosensitivemember, a means for receiving a toner, a means for supplying the tonerto develop the electrostatic latent image on the surface of thephotosensitive member, thereby forming a toner image, and a means fortransferring the toner image from the surface of the photosensitivemember to a transfer medium, wherein the means for receiving the tonercontains a polymerized toner of core-shell structure, comprising coreparticles composed of colored polymer particles which contain a compoundhaving at least one >C═N⁺< structure in its molecule and a colorant, anda layer of a polymer having a glass transition temperature higher thanthat of a polymer component making up the core particles, said polymerlayer covering each of the core particles.